This invention relates to a plate nut assembly used to fasten an instrument or the like to a wall or the like, to a back of which hands cannot reach.
When an instrument or the like is bolted to such a member, a plate nut assembly is used. As disclosed in Japanese patent publication 10-306818, the plate nut assembly includes a rectangular plate-like nut having a threaded hole extending in a thickness direction of the nut, and a bendable support tongue piece fixed to the nut. A tool or instrument is fixed to a wall by forming a circular hole in the wall, inserting the nut through the circular hole to a back side of the wall, pulling back the support tongue piece in a direction away from the wall so as to press the nut against the back side of the wall, and threading a bolt through the instrument or tool into the threaded hole of the nut.
When such a plate nut assembly is used, an outer diameter of the bolt to be threaded into the nut is limited to a rather small value as compared to a diameter of the circular hole formed in the wall. Thus, if an external force is applied in a direction perpendicular to an axis of the bolt after mounting of the instrument or tool to the wall, the axis of the bolt tends to be displaced in a direction of the external force until the bolt abuts a peripheral edge of the circular hole, with the bolt and the plate nut assembly in threaded engagement with each other.
In order to prevent such displacement, with a conventional plate nut assembly, a protrusion protruding in a steplike manner is provided around an entrance of the threaded hole of the nut on one side thereof. After inserting the nut into a circular hole in the wall, when the support tongue piece is pulled in a direction away from the wall so as to press the nut against the back side of the wall, the protrusion fits within the circular hole formed in the wall.
However, since the protrusion on the nut of the conventional plate nut assembly is formed of such a shape that protruding surfaces protrude in the form of flat steps, although sought after effects are realized if the protrusion fits snugly in the circular hole of the wall or the like, the protrusion has no guiding function in centering the nut relative to the circular hole to ensure that the threaded hole will be coaxial with respect to the circular hole. Thus, as described above, when the nut is pressed against the back side of the wall by pulling back the support tongue piece in a direction away from the wall, the protrusion abuts the back side of the wall, so that the nut may be displaced relative to the circular hole.
An object of this invention is to provide a plate nut assembly in which a protrusion provided on a nut has a guiding function in centering the nut relative to a circular hole in a wall so that a threaded hole of the nut will be coaxial with respect to the circular hole and the protrusion will reliably fit within the circular hole so as not to be displaced in a direction of an external force, even if the external force is applied in a direction perpendicular to an axis of a bolt in threaded engagement with the threaded hole.
According to this invention, there is provided a plate nut assembly comprising a rectangular plate-like nut formed with a threaded hole extending in a thickness direction of the nut, and a support tongue piece having one end thereof fixed to the nut at a corresponding end thereof. A protrusion is formed on one side of the nut around the threaded hole, so that a height of the protrusion decreases in a direction away from the threaded hole, and a recess having substantially the same outer shape as that of the protrusion is formed around the threaded hole on another side of the nut. The recess has opposed end walls that are inclined such that a distance between the opposed end walls decreases in a direction toward a bottom of the recess.
According to this invention, by forming a recess on the other side of the nut by performing a pressing operation, material of the nut swells toward the one side, thereby forming the protrusion on the one side of the nut. Thus, it is possible to economically produce the nut.
Also, by inclining the opposed end walls of the recess on the other side of the nut so that the distance between the opposed end walls decreases in a direction toward the bottom of the recess, it is possible to prevent a pressing pressure, for forming the recess, from locally concentrating on the protrusion formed on the one side of the nut, and to prevent an internal structure of the nut from being destroyed along an outer contour of the nut.